纳米改性Ti(C,N)基金属陶瓷的抗热震性能研究

为研究不同金属相对纳米TiN改性Ti(C,N)基金属陶瓷抗热震性能的影响,采用真空烧结法分别制备了Ti(C,N)基20Ni、10Co-10Ni和20Co三组金属陶瓷,用急冷-强度法测定了其抗热震性能.结果表明,3组金属陶瓷试样的热震残留强度均随热震温度的升高而降低,其热震残留强度急剧下降的临界温度分别为410、370和330℃.扫描电镜分析结果表明,热震后试样的组织仍然保持着金属陶瓷典型的芯/壳结构,随着热震温度的升高,组织中出现裂纹,断口中有气孔及裂纹出现,导致材料强度下降.对热震试样硬度的测试结果表明,纳米TiN改性Ti(C,N)基金属陶瓷在热震后仍然具有很高的硬度.     

纳米TiN改性Ti(C,N)基金属陶瓷的抗热震性能

为研究不同粘结相对纳米TiN改性Ti(C,N)基金属陶瓷抗热震性能的影响,真空烧结制备了粘结相质量分数分别为20%Ni、10%Co-10%Ni和20%Co的Ti(C,N)基金属陶瓷。采用扫描电镜研究了材料的组织,并测量了力学性能。采用压痕-急冷法主要研究了其抗热震性能,结果表明,随着温度的升高和热循环次数的增加,裂纹增长,粘结相为Ni的金属陶瓷的抗热震性优于粘结相为Co的金属陶瓷。显微照片表明,裂纹主要沿硬质相/粘结相界面及粘结相扩展。     

Ti(C,N)基金属陶瓷成分对抗热震性能的影响

制备了不同碳氮比Ti(C,N)固溶体和分别加入NbC、TaC、VC、Cr₃C₂的Ti(C,N)基金属陶瓷，采用水淬冷热震方法研究了不同成分对Ti(C,N)基金属陶瓷抗热震性能的影响。结果表明：金属陶瓷在热冲击过程中，陶瓷相在热应力的作用下会发生开裂现象，在裂纹扩展路径上产生的微裂纹能促进裂纹扩展；在不同碳氮比的Ti(C_x,N_y)固溶体金属陶瓷中，碳氮比7/3的Ti(C_0.7,N_0.3)金属陶瓷的抗热震性能最好，本文研究中其热震临界温度为240℃；在添加的四种碳化物(NbC、TaC、VC和Cr₃C₂)中，NbC和TaC能显著提升金属陶瓷的抗热震性，且TaC更优于NbC，而VC和Cr₃C₂的加入不利于改善金属陶瓷抗热冲击性能。     

碳纳米管增韧Ti(C,N)基金属陶瓷的制备及抗热震性能

采用粉末冶金真空烧结法制备了添加1.0 wt%碳纳米管的Ti(C,N) -WC -Co金属陶瓷,用压痕-急冷法研究了其抗热震性能.实验结果表明,添加1.0 wt%碳纳米管的Ti(C,N)-Co金属陶瓷材料比未添加碳纳米管的金属陶瓷抗热震性能好,碳纳米管的增韧效果是产生这一现象的主要原因;随着温度的升高和热循环次数的增加,热震裂纹扩展率增长.     

渗硼对Ti(C,N)基金属陶瓷抗热震性能的影响

采用粉末冶金法制备了Ti(C,N)基金属陶瓷,并对其进行了固体渗硼。研究了渗硼后金属陶瓷的显微组织和力学性能以及渗硼对抗热震性能的影响。结果表明,Ti(C,N)基金属陶瓷的渗硼层由硼化物层、扩散层和基体区组成;渗硼使金属陶瓷的表面硬度提高,抗弯强度降低,使导致金属陶瓷热震残留强度急剧下降的临界热震温差降低约100℃;渗硼使Ti(C,N)基金属陶瓷热震后的残留强度降低,主要是分布不均和形状不规则的孔洞所致;当热震温差较小时,渗硼使金属陶瓷表面萌生热震裂纹的孕育期延长,从而推迟了主裂纹的形成;而热震温差较大时,经渗硼的金属陶瓷热震裂纹扩展较快,易形成龟裂。     

ZrC添加量对Ti(C,N)基金属陶瓷组织结构及耐腐蚀性能的影响

通过在Ti(C,N)-WC-Nb C-Co-Ni金属陶瓷中加入ZrC,研究了ZrC不同添加量对Ti(C,N)基金属陶瓷微观组织、力学性能及其在2 mol/L盐酸中的耐腐蚀性能的影响。实验结果表明,在碳氮化钛基金属陶瓷中适量的ZrC添加将会与Nb C产生协同作用,在抑制脆性固溶体壳相厚度的同时,能够促使铌元素通过固溶强化及金属间化合物弥散强化的形式对粘结相进行增强,提高了材料力学性能及耐腐蚀性能。当ZrC过量加入达到10%时,金属陶瓷材料的显微组织发生突变,主要由粘结相及白芯灰壳结构组成,同时粘结相中铌元素含量减少,力学性能及耐腐蚀性能均大幅度下降。实验试样中,含有1%ZrC的金属陶瓷试样抗弯强度达到2 550 MPa,并且有最高的断裂韧性13.0 MPa·m~(1/2)。     

钼含量对Ti（C，N）-Co金属陶瓷抗热震性能的影响

采用真空烧结工艺,以纳米TiN、亚微米TiC等陶瓷粉体作原材料,以金属钴作粘结剂,并添加不同含量钼,制备了Ti（C,N）-Co金属陶瓷。采用扫描电镜研究了Ti（C,N）-Co金属陶瓷的组织,测量了力学性能,采用压痕．急冷法研究了抗热震性能。结果表明,随着热震温度的升高和热循环次数的增加,金属陶瓷中的裂纹增长;钼含量较低的Ti（C,N）-Co金属陶瓷抗热震性能较好。     

相含量的变化对氧化锆陶瓷性能的影响

研究了氧化钇含量对氧化锆陶瓷相含量和性能的影响 ,分析了性能变化的原因和传统抗热震理论的不足 ,同时简化了急热急冷条件下抗热震系数的计算。结果显示 :氧化钇含量为 2 5mol,%时 ,15 80℃× 1h常压烧结的氧化钇稳定氧化锆陶瓷的抗热震性最佳 ;氧化钇含量为 3 0mol,%时 ,材料的综合力学性能最佳 ;氧化钇含量为 3 5mol,%时 ,材料的线膨胀系数最大 ;在急热急冷条件下 ,对于相组成不同的同种材料而言 ,材料的抗热震性可简单表述为抗弯强度和线膨胀系数的函数     

ZrB2-20％SiC超高温陶瓷抗热震性能研究

采用放电等离子烧结工艺在1850℃烧结温度、升温速度200℃／min、保温3min、压力50MPa条件下制备了ZrB2—20％SiC（体积分数，下同）超高温陶瓷材料。通过不同温度下单次和5次重复热震（水淬试验）后测试材料的残余强度来评价ZrB2一SiC陶瓷材料的抗热震性能，通过SEM分析研究材料的热震损伤机制。研究结果表明，随着热震温度的提高，ZrB2-SiC材料热震后的残余强度逐渐降低，但1400℃热震后形成的玻璃相，对裂纹有修补、愈合的作用，提高了试样的残余强度。单次热震的损伤机制主要是微裂纹的产生。5次热震后试样的残余强度与相同温度下的单次热震相比要低很多，5次热震的损伤机制是氧化和微裂纹的共同作用。ZrB2-SiC材料的抗热震试验结果显示了该材料具有优异的抗热震性能。     

锂辉石/SiCp紫砂陶的抗热震性能

采用水冷-强度法测试表征了锂辉石/SiCp紫砂陶试样抗热震性能,结合SEM、XRD等测试分析手段进行物相、微观组织形貌方面分析,在SiCp含量为9%条件下,重点研究锂辉石含量(0~32%)对紫砂陶试样力学和热学性质的影响。结果表明,锂辉石含量为16%时,紫砂陶试样抗折强度达到最大值83.37 MPa;含量为24%时,平均热膨胀系数最低,强度保持率达到53.07%最高值,抗热震性能最好;莫来石和β-锂辉石固溶体晶相含量随锂辉石含量增大而增多;试样热震后断口出现裂纹,沿晶断裂是试样断裂的主要方式。     

循环条件对金属陶瓷热冲击疲劳的影响

研究了循环条件对40％Ni－Ti（C,N）金属陶瓷热冲击疲劳的影响。结果表明,循环条件对金属陶瓷热冲击疲劳有很大影响。随循环温度和冷却速率的增加,裂纹形核的孕育期缩短,裂纹扩展速率增加。扫描电镜观察发现,断口形貌中存在疲劳条纹。     

Thermal Shock Resistance of Si<Subscript>3</Subscript>N<Subscript>4</Subscript>/h<Emphasis Type="Italic">-</Emphasis>BN Composites Prepared via Catalytic Reaction-Bonding Route

Si₃N₄/h-BN ceramic matrix composites were prepared via a catalytic reaction-bonding route by using ZrO₂ as nitridation catalyst, and the water quenching (fast cooling) and molten aluminum quenching tests (fast heating) were carried out to evaluate the thermal shock resistance of the composites. The results showed that the thermal shock resistance was improved obviously with the increase in h-BN content, and the critical thermal shock temperature difference (ΔT _c) reaches as high as 780 °C when the h-BN content was 30 wt.%. The improvement of thermal shock resistance of the composites was mainly due to the crack tending to quasi static propagating at weak bonding interface between Si₃N₄ and h-BN with the increase in h-BN content. For the molten aluminum quenching test, the residual strength showed no obvious decrease compared with water quenching test, which could be caused by the mild stress condition on the surface. In addition, a calculated parameter, volumetric crack density (N _f), was presented to quantitative evaluating the thermal shock resistance of the composites in contrast to the conventional R parameter.     

40%Ni—Ti（C,N）金属陶瓷热冲击疲劳的研究

对４０％Ｎｉ－Ｔｉ（Ｃ,Ｎ）金属陶瓷在热冲击条件下缺口试样裂纹的形成及扩展进行了研究。结果表明,裂纹的形成存在孕育期,且随循环温度的升高,孕育期缩短,扩展速率增加;裂纹的形成与组织中陶瓷相／金属相界面微孔洞的形成有关。扫描电镜观察发现,断口形貌中存在着疲劳条纹,断裂沿陶瓷相／金属相界面及金属相中进行     

Effect of adding methods of metallic phase on microstructure and thermal shock resistance of Ni/（90NiFe2O4-10NiO） cermets

Ball mixing and electroless plating were respectively used as the adding methods of metallic phase to prepare Ni/（90NiFe2O4-10NiO） cermets for the inert anode in aluminum electrolysis. The microstructure and thermal shock resistance of cermet samples were studied. The results show that, for the samples prepared by ball mixing method, aggregation of metallic phase is found in either the green blocks or sintered samples and the extent of aggregation increases with the increase of metal content. For 6.5Ni/（90NiFe2O4-10NiO） cermets prepared with electroless plating method, the homogeneous and fine metallic particles are found in either the green compacts or sintered samples, but the relative density and thermal shock residual strength decrease by 3% and 28%-58% respectively, compared with samples prepared with ball mixing method.     

Thermal shock resistance of ceramic coatings

A methodology is established for the evaluation of the thermal shock resistance of ceramic coatings. The problem is formulated by considering a thin coating to a thick substrate subjected to a sudden cooling on the coating surface. Time-varied thermal stresses and stress intensity factors for various parameters of the problem are obtained. The crack initiation behavior and the thermal shock resistance of the coating are studied. The crack length dependency behavior of the thermal shock resistance of the coating is discussed. Two critical size parameters, which control the applicability of the stress-based criterion and the fracture mechanics-based criterion to the determination of the thermal shock resistance of coatings, are explored.     

FAILURES AND THE LIFE OF FURNACE TUBES

It is showed after the furnace tubes serviced for 8-10 years that the density of damage in the HAZ (heat affected zone) of the weld has higher than in parent metals, though the depth of damage is not equal to. By the test of creep crack growth, it is also acquired that under same mechanic parameter C* (t), the rate of creep crack growth in the HAZ is more than twice as fast as in parent metals. Two mechanisms (overheating and thermal shock) of failure occurred in an accident are presented. The stress of thermal shock is analyzed, in which the change of the elasticity modulus with the radius ET=f(r) is considered. Based on it, the safety region of the thermal shock is obtained. Finally, two sets of curves for the safe life are suggested which can facilitate to estimate the remainina life of HK-40 or HP-Nb tubes by their creep rupture data.     

梯度金属陶瓷(TiC)pNi与Ti燃烧扩散连接界面组织及力学性能

采用MA-FAPAS工艺,借助中间层TiAl的燃烧反应放热,原位合成了梯度金属陶瓷(TiC)pNi和金属间化合物TiAl,并同步完成了(TiC)pNi/TiAl/Ti的扩散连接,研究了在外加温度场、电场和应力场耦合作用下连接结构的形成机制.利用FE-SEM、TEM和XRD等手段对各层及连接界面的微观结构和相组成,以及电场作用下各连接界面元素扩散特征进行分析;采用显微硬度压痕法对连接界面的韧性进行分析;采用剪切法、冷淬法和有限元法对界面结合强度和残余应力分布进行分析计算.结果表明,各燃烧层均发生充分反应并形成了良好的冶金结合,连接界面处存在强烈的元素交互扩散;连接界面具有较强的抗剥离和抗剪切强度,(TiC)pNi/TiAl界面为接头的薄弱环节.     

Crater wear mechanisms of TiCN–Ni–WC cermets during dry machining

TiCN–Ni-based cermets are attractive cutting tools because of the combination of high hardness and wear resistance with improved toughness and thermal shock resistance. The present work reports the effect of WC addition (0–15 wt.%) on the machining performance of TiCN–20 wt.% Ni cermets against boiler steel. The cutting force was measured on-line using dynamometer, with respect to varying cutting speed and feed rate, in dry and orthogonal cutting conditions. The principal aim of the present investigation is to evaluate the dominant mechanisms, responsible for material removal on the rake face of cermets, using SEM–EDS. The cutting performance of TiCN–Ni cermet is observed to improve with the addition of WC content upto 10 wt.%. While, the adhesion of tribochemical layer is dominant with limited WC content, the presence of abrasive grooves and pull-outs are observed for TiCN–20Ni cermets containing higher amount of WC (>10 wt.%).